Jump to content

GT6 Cylinder Head Question


Mike T
 Share

Recommended Posts

Hi

I have just removed the head from my GT6 MkIII to try and cure a leaking head gasket. Whilst I have the head off I plan to get it converted to unleaded. Last year I picked up a spare head which I think is from a TR6. The current head is stamped 218225 and the spare head 516816. They both have the same valve size and other than the TR6 head having double valve springs they seem to be the same. My question is which head to do the work on, is there any advantage with the TR6 head over the GT6 head. I am not planning any change to the camshaft at this stage so I assume double valve springs don't offer any benefits.

Any advice would be most welcome

 

Mike

Link to comment
Share on other sites

Mike,

Scan the web for the two head numbers, it looks like there might be compression ratio issues with replacing one with the other.

But, unless the valve seats are damaged there is little advantage in spending money having them unleaded. Search the web for "The memory of lead". The valve seats have been coated with lead and will do many thousands of miles before you start to get valve seat recession, if ever. 

Doug

Link to comment
Share on other sites

Hello Mike, The number on the head, 218225, is correct for a late Mk3 GT6. The engine should also have domed pistons. Many engine reconditioners now fit single valve springs to reduced the wear on the cam. Double valve springs are used to reduce valve bounce at high revs. Therefore unless you are going to frequently rev the engine to 6,000 rpm and above there should be no difference in the performance.

Dave

Link to comment
Share on other sites

Hi mike, I recently had some issues swapping around heads on a vitesse engine, I would suggest checking the overall head height as the dome piston head is slightly taller than flat piston variety, which ultimately affects the compression ratio. Flat pistons with taller head will have bad low compression, and shorter head with domed pistons will have too high compression, I would stick with the mk3 one if it was me, don’t forget to put some gasket sealant around the head gasket near the conrod holes ( Edge furthest away from pistons the distributor side) as I assumed skimming both head and block would be fine! Gonna have to do it again as leaking down the side of the block, doh! If only I read the forum more often. 

Good luck

hag 

Link to comment
Share on other sites

Hi

Thanks for the answers. You are correct the engine has domed pistons. I checked the height both heads and they are exactly the same. On the basis that there appears to be little difference between the heads I will use the head that was on the engine as it was running fine other than leaking. 

With respect to using sealant plus the gasket could you provide a little more information. What sort of sealant would you suggest and would you use on both sides of the gasket?

Mike

Link to comment
Share on other sites

Most compostie / copper gaskets are fitted  dry  as they need to grip, and not have any slippy stuff on them 

But as the head pants there can be leaks from the pushrod chest side and a light smear along this outer edge 

can work ok  ,

you, need a small smear around the oil feed hole to the rear rocker pedestal.  Only a smear , dont block this small hole

Always used heavy duty nuts and hard washers , certainly sold by canley's

Any standard nut will strip whether its  a 3/8" mk1 or 7/16"  mk2   , the head nuts are a much higher spec .

Bet your old washers are deformed by the load on the nut  have a close look at them, , this looses torque and allows early re failure

Do  a retorque after a few good miles 

Pete

Link to comment
Share on other sites

The washer comments explain why when I came to undo the head nuts they were not as tight as I was expecting. I suspect they were not clamping the head that tightly. There washers I have taken off were different sizes and thickness.

I will follow the suggested advice on use of sealant. 

Mike

Link to comment
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
 Share

×
×
  • Create New...